1. Field of the Invention
The present invention relates to a position sensor for an output shaft and, in particular, to a position sensor for an output shaft of a rotary actuator used in a shift and throttle system for marine vessel.
2. Description of the Related Art
It is well known to provide marine vessels with electronic shift and throttle systems to remotely control shift and throttle functions of a propulsion engine such as an outboard or inboard engine. In such systems it is desirable to know the position of a shift arm and/or throttle arm to prevent damage to the engine and assist in shifting. This is typically done using a position sensor which signals the position of the arm to a control circuit. To minimize differences between the actual position of the arm and the position of the arm sensed by the position sensor it is generally required that the position sensor be disposed within or adjacent to the actuator which actuates the arm.
For example, U.S. Pat. No. 7,335,070 issued on Feb. 26, 2008 to Yoda et al. and the full disclosure of which is incorporated herein by reference, discloses an remote control shift and throttle system comprising a shift actuator mounted an outboard engine. The shift actuator has a motor which rotates a worm gear which, in turn, engages a spur gear mechanism thereby imparting rotation to an output shaft. One of the spur gears in the spur gear mechanism is integrated with a potentiometer. Said one of the spur gears is also coupled to a microswitch which is wired to a control circuit. Together the potentiometer and microswitch function as a position sensor for sensing the position of a shift arm which is driven by the output shaft.
When the shift arm is in a neutral position, the spur gear engages the microswitch in a manner such that the microswitch is switched on. The microswitch signals a control circuit allowing the engine to be started by a starter switch. The potentiometer detects rotation of the spur gear as the shift arm is moved from the neutral position to either the shift forward position or shift reverse position. The motor is stopped by the control circuit when the potentiometer detects that the shift arm has moved to the shift forward position. Similarly, the motor is stopped by the control circuit when the potentiometer detects that the shift arm has moved to the shift reverse position. Stopping the motor when the shift arm is in either the shift forward or shift reverse position prevents the shift arm from breaking as a result of a high voltage being applied to the motor in the event of an electrical malfunction.